The present invention relates to cages for use in ball bearings which are useful, for example, for motor vehicle components, such as tensioners and electromagnetic clutches, and electric devices such as hard discs, fan motors and cleaners.
Ball bearing cages heretofore used are made of plastics or metal and are crown-shaped cages, ribbon-type pressed cages or annular molded cages. These cages are formed with a plurality of pockets each having an inwardly curved spherical face which is similar to the ball in shape and slightly greater than the ball in the radius of curvature. The pockets in the molded cage are each in the form of a through hole.
However, the conventional cages have the problem of causing the ball bearing to give off a noise during rotation when a highly viscous lubricant is applied to the ball bearing to prolong the life thereof or when the bearing is designed for high-speed rotation.
Accordingly, we have conducted various experiments and research to trace the cause for producing the noise and found that the noise is attributable to the following reason. When the rotatable ring of the ball bearing rotates relative to the fixed ring thereof, each ball is in sliding contact with the pocket face of the cage. With reference to FIG. 24, at a front portion of the rotatable ring 42 with respect to the direction of rotation thereof, the ball 40 which is revolving while rotating about its own axis pushes the pocket face 41, forming between the surface of the ball 40 and the pocket face 41 a clearance C which is generally uniform from the rotatable ring side toward the fixed ring (43) side. If the clearance C diminishes from a predetermined value in the case where the lubricant has a high viscosity or the rotatable ring 42 is in rotation at a high speed, the viscosity resistance of the lubricant present between the ball 40 and the pocket face 41 increases, offering greater resistance to the sliding contact to result in a noise.
Another problem is also encountered in that the increased resistance to the sliding contact stated above makes the ball bearing require higher torque for rotation. The increased resistance to the sliding contact further entails the problem of heating the lubricant to a high temperature to shorten the life of the lubricant.